Frontal lobe seizure propagation: Scalp and subdural EEG studies

Purpose: To study propagation properties of focally originating frontal lob e seizures: principally direction and promptness of ictal spread. Method: Forty-eight scalp EEG-recorded and 17 subdurally recorded seizures in two separate groups of patients were visually scrutinized. Results: Initial propagation was directed more commonly to contiguous front al cortex than to the opposite hemisphere in both studies: 58% and 86% for scalp and subdural recordings, respectively. Eighteen (38%) of scalp EEG se izures propagated within 5-10 s of apparent onset, whereas 16 (33%) did so after 11-20 s; no evidence of propagation could be discerned in the remaini ng 14 (29%). Of subdurally recorded attacks, only four (24%) propagated in the first 4 s: six (35%) did so after a delay of 5-10 s; six (35%) either f ailed to propagate or did so after greater than or equal to 20-s latency. L atency to initial propagation was between 5 and 20 s in 41 (63%) of the 65 seizures in both studies. Ictal activity remained within the frontal lobe o f origin for greater than or equal to 10 s in 39 (81%) of scalp-recorded se izures and 11 (65%) of subdural seizures. It remained so confined for great er than or equal to 15 s in 26 (54%) and nine (53%), respectively. Twenty-f our (50%) of scalp-recorded seizures displayed evidence of opposite hemisph ere (bisynchronous or other contralateral) involvement, occurring 5-10 s af ter onset in eight (17%) seizures and 10-20 s after onset in 16 (33%). Simi larly, the subdural study documented spread to the opposite hemisphere in 1 1 (65%) of seizures with a latency ranging from 1 to 45 s. Conclusions: Frontal lobe seizures in this study propagated less promptly t han reputed, and initial spread occurred more commonly to the frontal lobe of origin than to the opposite hemisphere. Such properties underlie the goo d lateralizing value of clinical semiology of frontal lobe seizures.